IIRC there are rules that any catastrophic engine failure must be contained. The Concord was granted an exception and that didnt go so well. Degree going out the back and hitting hydraulics was the cause of some other incident like Sioux City Iowa.
The engine placement is also problematic for maintenance. Airlines prefer to buy aircraft that their mechanics can service with just a short ladder. That's one of the main reasons why all recent designs have engines only under the wings.
Engines have taken out hydraulic control lines in the past.